This invention relates generally to electrical fuses, and more specifically, to an electrical safety connector fuse having a plug intended for insertion into an outlet or socket of a domestic or similar electrical system, the connector fuse being intended to receive a plug to provide additional safety.
Conventional electrical systems used to provide electrical power (e.g. 110/220 V in US) in residences and other buildings use circuit breakers to provide protection against short circuits or similar malfunctions in the electrical system itself or in equipment attached thereto. Typically, a single set of wires enters a residence and is connected to a circuit breaker box containing a plurality of circuit breakers, each of which is connected to one of a plurality of electrical circuits which radiate out from the box. Each of these circuits supplies power to several different wall outlets, light fittings or other electrical devices. One or more or the circuit breakers within the box may be of the ground fault interrupter type to provide additional safety to outlets in bathrooms or outside the house, where they may be exposed to water.
Although circuit breakers are effective in preventing damage from many electrical malfunctions, they suffer from several problems. Firstly, the circuit breakers themselves are mechanical devices which may fail to open when a current greater than their rated load passes through them. Such failures may be caused, for example, by corrosion or accumulation of dirt and debris within the circuit breaker, especially since circuit breakers in private houses are rarely if ever inspected by professional electricians. Secondly, although the rating of a circuit breaker can be varied for the intended use of the circuit connected thereto, each circuit breaker typically controls several electrical outlets. Therefore, the circuit breaker may not be specific to each outlet or appliance, but instead supplies to the circuit as a whole. For example, a single outlet in a kitchen might be used to power both an under-cabinet fluorescent lamp, drawing less than 20 W, and an electric kettle, drawing 1500 W. A malfunction in the lamp which caused it to draw 500 W might well be dangerous, but would not trip the associated circuit breaker, which must be able to pass the 1500 W required by the kettle. Finally, circuit breakers, being mechanical devices, may not respond quickly enough to prevent an accidental electrocution.
In addition to the hazards of electrocution, there is the ever present danger of fires caused by overloaded circuits and/or shorting failures in appliances attached to circuits.
For the foregoing reasons, many experts believe that fuses placed adjacent each appliance provide better safety protection than centrally located circuit breakers, and personal computers and other expensive consumer electronics are often sold with internal fuses. However, such fuses give rise to additional problems. Laymen may well be unaware that such fuses are present, and there is no indication on the exterior of the electronic device when the fuse has blown; the electronic device simply stops working. Also, even if the owner of the device discovers the blown fuse, the fuses are not well standardized, so there may be difficulty and delay in procuring a replacement fuse.
In view of these known disadvantages of both circuit breakers and internal fuses, so-called xe2x80x9cfused connectorsxe2x80x9d have been developed. Such fused connectors are described for example in U.S. Pat. No. 3,218,413 (Koch); U.S. Pat. No. 3,320,383 (Koetter); U.S. Pat. No. 3.924,914 (Banner); U.S. Pat. No. 4,178,061 (Ahroni); U.S. Pat. No. 4,575,704 (Pezold); and U.S. Pat. No. 5,137,473 (Nickola). Essentally, a fused connector comprises a conventional plug adapted to plug into an electrical socket and is provided with a socket into which the plug of an appliance is inserted. A fuse is connected between the prongs of the connector fuse and the socket so that if the appliance draws too much power the fuse will blow. The rating of the fuse can be varied depending upon the type of appliance with which the connector fuse is intended to be used. The aforementioned Banner patent suggests that a small lamp be connected between the live and neutral lines with the fused connector such that the light will be lit when the connector is inserted into an electrical socket but will go out when the fuse blows, thus providing a visual indicator of a blown fuse.
Known fused connectors suffer from several disadvantages. The fuse is accessible to users so that it is possible for a user to replace the original fuse with one having a different rating. Consequently, there is usually no visual indication of the rating of the fuse within the connector, which renders it difficult for the user to select a connector having a fuse rating appropriate for the particular appliance with which it is to be used. Also, when the connector is inserted into a socket, there is nothing to prevent a child from (or perhaps an incautious adult wielding a screwdriver) inserting a narrow metal object into the live receptacle intended to receive the live prong of a plug, and the child may receive a dangerous, and perhaps even fatal, electric shock before the fuse blows. In addition, some users, when inserting the fused connector into a socket, tend to hold it by the portion adjacent the prongs, and it is easy for the user""s fingers to contact the live prong as it is being inserted into the socket, thus giving the user an electric shock. Finally, many fused connectors fail to provide any visual indication that a fuse has blown.
Consequently, it is a primary object of the present invention to provide an electrical safety connector which overcomes these disadvantages of prior art fused connector.
It is a further object of the present invention to provide a safety connector fuse which can provide a reliable indication of the rating of the fuse therein.
It is a further object of the present invention to provide a safety connector fuse which can provide a reliable indication when its fuse has blown.
It is a further object of the present invention to provide a safety connector fuse which renders it difficult for a user to suffer an electric shock by insertion of an object into the apertures intended to receive the plug of an electrical appliance.
It is a further object of the present invention to provide a safety connector fuse which renders it difficult for a user to suffer an electric shock as the safety connector fuse is being inserted into a socket.
Other objects of the invention will be apparent and will appear hereinafter in the following detailed description when read in connection with the drawings.
This invention provides an electrical safety connector fuse for insertion into a standard electrical socket having at least live and neutral prong receptacles. The safety connector fuse comprises a sealed, tamper-proof housing having live and neutral apertures arranged to receive the live and neutral prongs, respectively, of an electrical plug. The connector fuse further comprises live and neutral prongs extending outwardly from the housing at points spaced from the live and neutral apertures, the live and neutral prongs being arranged to engage the live and neutral prong receptacles, respectively, of an electrical socket, or the like. A fuse is disposed within the housing and electrically connected to its live prong. The connector fuse also comprises a live receptacle electrically connected to the fuse, and disposed within the housing adjacent the live aperture therein so as to engage the live prong of a plug passing through the live aperture, and a neutral receptacle electrically connected to the neutral prong, and disposed within the housing adjacent the neutral aperture therein so as to engage the neutral prong of a plug passing through the neutral aperture.
In the connector fuse of the present invention, at least part of the housing may be light-transmissive, and the connector fuse may be provided with means for emitting light disposed within the housing and adjacent the light-transmissive portion thereof, so that light emitted from the light emitting means is visible outside the housing, the light emitting means being electrically connected to the live and neutral receptacles so as to emit light when a potential difference exists between these receptacles.
Also, the connector fuse in one aspect may comprise a blocking member disposed within the housing adjacent the live and neutral apertures therein, the blocking member having a neutral aperture extending therethrough and being movable between a closed position, in which it blocks the live and neutral apertures in the housing, and an open position, in which the neutral aperture of the blocking member is aligned with the neutral aperture of the housing, thereby allowing the live and neutral prongs of the plug to pass through the live and neutral apertures in the housing and engage the live and neutral receptacles within the housing. The blocking member is provided with biasing means for continuously biasing the blocking member towards its closed position. The blocking member also has a cam surface disposed adjacent its neutral aperture and arranged to be engaged by the neutral prong of the plug passing through the neutral aperture in the housing, so that contact between the neutral prong and the cam surface causes the blocking member to move to its open position under the force applied by the bias spring. The blocking member may be provided with a recess arranged so that, when the blocking member is in its closed position, the recess will lie adjacent the live aperture of the connector fuse, so that a portion of the live prong of a plug can be accommodated within the recess while the blocking member is still in its closed position.
Also, the neutral prong of the connector fuse of the present invention may extend a greater distance from the housing than its live prong.
In another preferred form of the present safety connector fuse, the live prong has an outward surface facing away from the neutral prong of the connector fuse, and at least a portion of this outward surface is formed from an electrically insulating material.
For reasons explained in detail below, the usefulness of providing electrically insulating material on the live prong of a plug is not confined to safety connector fuses. Thus, in another aspect, this invention provides an electrical plug having a housing and live and neutral prongs extending therefrom, the live prong having an outward surface facing away from the neutral prong, and at least a portion of this outward surface being formed from an electrically insulating material.
The connector fuse of the present invention provides several safety features. The sealed, tamper-proof housing prevents user replacement of the fuse so that a user can be confident that any markings on the plug accurately indicate the rating of the fuse contained therein, thus assuring that the user can select an appropriately rated connector fuse for a particular appliance. The extra length of the neutral prong of the plug (when present) as compared with its live prong, ensures that the neutral prong will make contact with the neutral receptacle of the socket before the live prong of the plug makes contact with the live receptacle, so that the live receptacle of the connector fuse cannot go live before an appropriate connection has been made with the neutral line. The blocking member ensures that a user cannot receive an electric shock by inserting a narrow metal object into the live aperture in the connector fuse. The provision of electrically insulating material on the outward surface of the live prong helps to ensure that a user will not receive an electric shock by-accidentally touching electrically conductive material in the live prong of the connector fuse as the fuse, or similarly equipped plug, is being inserted into a socket, as it is being pulled out of a socket, or is only partway in a socket.